Using CTL epitopes to the Ebola GP, NP, VP24, VP30, VP35 and VP40 virion proteins, a method and composition for use in inducing an immune response which is protective against infection with Ebola virus is described.
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3. A composition comprising the isolated peptide of seq ID NO: 29 or an isolated peptide consisting of seq ID NO:42, in an effective immunogenic amount in a pharmaceutically acceptable carrier and/or adjuvant.
4. An immunogenic composition comprising the isolated peptide of seq ID NO: 29 or an isolated peptide consisting of seq ID NO:42, in an effective immunogenic amount in a pharmaceutically acceptable carrier and/or adjuvant.
5. A composition comprising recombinant virus replicon particles expressing the peptide of seq ID NO:29 or an isolated peptide consisting of seq ID NO: 42, in an effective immunogenic amount in a pharmaceutically acceptable carrier and/or adjuvant.
1. An isolated glycoprotein (GP) Ebola peptide comprising the sequence specified in seq ID NO:29, or consisting of an isolated peptide fragment of seq ID NO:29 comprising at least 9 consecutive amino acids which includes the amino acid threonine corresponding to position 14 in seq ID NO:29.
6. The composition of
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This application is a continuation-in-part of U.S. utility application Ser. No. 09/337,946, filed Jun. 22, 1999 now abandoned, which claims priority from U.S. provisional application 60/091,403 (filed Jun. 29, 1998). The entire contents of both applications are incorporated herein by reference.
Ebola viruses, members of the family Filoviridae, are associated with outbreaks of highly lethal hemorrhagic fever in humans and nonhuman primates. The natural reservoir of the virus is unknown and there currently are no available vaccines or effective therapeutic treatments for filovirus infections. The genome of Ebola virus consists of a single strand of negative sense RNA that is approximately 19 kb in length. This RNA contains seven sequentially arranged genes that produce 8 mRNAs upon infection (
Recent studies using rodent models to evaluate subunit vaccines for Ebola virus infection using recombinant vaccinia virus encoding Ebola virus GP (Gilligan et al., (1997) In Vaccines 97, pp. 87-92. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.), or naked DNA constructs expressing either GP or sGP (Xu et al. (1998) Nature Med. 4, 37-42) have demonstrated the protective efficacy of Ebola virus GP in guinea pigs. (All documents cited herein supra and infra are hereby incorporated in their entirety by reference thereto.) Additionally, Ebola virus NP and GP genes expressed from naked DNA vaccines (Vanderzanden et al.,(1998) Virology 246, 134-144) have elicited protective immunity in BALB/c mice. There has been one study that showed protection in nonhuman primates with a high dose DNA prime/high dose adenovirus boost and a 6 pfu challenge. However, this study provides limited benefit for humans or non-human primates because such high dosing is unlikely to be given to humans due to high inherent risks and other factors. So there still exists a need for a human vaccine which is efficacious for protection from Ebola virus infection.
The present invention satisfies the need discussed above. The present invention relates to a method and composition for use in inducing an immune response which is protective against infection with Ebola virus.
Because the biological functions of the individual Ebola virus proteins were not previously known and the immune mechanisms necessary for preventing and clearing Ebola virus infection were not previously well understood, it was not known which antigens significantly contribute to protection and should therefore be included in an eventual vaccine candidate to induce a protective immune response. However, the inventors have induced protection against Ebola infection in mammals using virus replicon particles (VRPs) expressing the Ebola GP, NP, VP24, VP30, VP35 or VP40 genes. These VRPs and some uses are described in co-pending application Ser. No. 09/337,946 (filed Jun. 22, 1999), the entire contents of which are hereby incorporated by reference.
One embodiment of the present invention entails a DNA fragment encoding each of the Ebola Zaire 1976 GP, NP, VP24, VP30, VP35, and VP40 virion proteins (SEQUENCE ID NOS. 1-7).
Another embodiment provides the DNA fragments of Ebola virion proteins in a recombinant vector. When the vector is an expression vector, the Ebola virion proteins GP, NP, VP24, VP30, VP35, and VP40 are produced. It is preferred that the vector is an alphavirus replicon vector, especially a replicon vector that has the ability to produce the desired protein or peptide in a manner that induces protective B and T cells in vivo in mammals. Any alphavirus vector may be effective, including but not limited to the Venezuelan Equine Encephalitis (VEE) virus, eastern equine encephalitis, western equine encephalitis, Semliki forest and Sindbis. For instance, in a preferred embodiment the VEE replicon vector comprises a VEE virus replicon and a DNA fragment encoding any of the Ebola Zaire 1976 (Mayinga isolate) GP, NP, VP24, VP30, VP35, or VP40 proteins. In another preferred embodiment, the VEE replicon vector comprises a VEE virus replicon and a DNA fragment encoding any of the amino acid sequences set forth in SEQ ID NOs:24-53. The construct can be used as a nucleic acid vaccine or for the production of self replicating RNA. To that end, a self replicating RNA of this invention can comprise the VEE virus replicon and any of the Ebola Zaire 1976 (Mayinga isolate) RNAs encoding the GP, NP, VP24, VP30, VP35, and VP40 proteins described above, or the amino acid sequences set forth in SEQ ID NOs:24-53. The RNA can be used as a vaccine for protection from Ebola infection. When the RNA is packaged, a VEE virus replicon particle is produced.
Another embodiment entails infectious VEE virus replicon particles produced from the VEE virus replicon RNAs described above.
Another embodiment of the invention encompasses peptides that make up cytotoxic T lymphocyte (CTL) epitopes corresponding to Ebola GP, NP, VP24, VP30, VP35, or VP40 proteins. The epitopes may include the sequences identified as SEQ ID NOS:24-53, as described below. A related aspect of this embodiment provides DNA fragments that respectively encode these Ebola peptides. A further embodiment relates to recombinant DNA constructs that express these epitope peptides.
An additional embodiment includes a pharmaceutical composition that includes one or more of these CTL epitope peptides (and preferably one or more of SEQ ID NOs:24-53), in an effective immunogenic amount in a pharmaceutically acceptable carrier and/or adjuvant.
A further embodiment entails an immunological composition for the protection of mammals including humans against Ebola virus infection, comprising at least one (but preferably at least two, and more preferably at least three, and most preferably all) of the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins. In a related embodiment, the composition may include one or more of the CTL epitopes set forth in SEQ ID NOs: 24-53 (described below).
In a related preferred embodiment, the immunological compositions comprise alphavirus replicon particles (such as, for instance, VEE virus replicon particles) expressing the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins, or any combination of different VEE virus replicons each expressing one or more different Ebola proteins selected from GP, NP, VP24, VP30, VP35 and VP40. For instance, in a preferred embodiment the composition may include one or more of SEQ ID NOs: 24-53 (described below). In another preferred embodiment, the composition includes at least the VP30, VP35 and VP40 proteins.
An additional embodiment includes vaccines against infection by Ebola , comprising virus replicon particles (preferably VEE virus replicon particles) expressing the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins, or any combination of different VEE virus replicons each expressing one or more different Ebola proteins selected from GP, NP, VP24, VP30, VP35 and VP40. For instance, in a preferred embodiment the Ebola VRPs contain one or more of the peptides specified by SEQ ID NOs: 24-53. In a related embodiment, the vaccine may include at a minimum at least one of the Ebola proteins selected from GP, NP, VP24, VP30, VP35 and VP40. For instance, in a preferred embodiment the vaccine includes at least the VP30, VP35 and VP40 proteins. In another preferred embodiment, the vaccine may include one or more of SEQ ID NOs: 24-53.
The invention also contemplates methods for inducing in a mammal a cytotoxic T lymphocyte response to the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins, or to a peptide comprising at least 6 amino acids thereof. In one version of the method, a recombinant DNA construct is administered to a mammal, such as, for example, a mouse, a guinea pig, a monkey or a human, which a recombinant DNA construct expresses the amino acid sequence of at least one of the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins (or a peptide comprising at least 6 amino acids thereof), under such conditions that a protective CTL response is induced in that mammal. In particular, the administered peptides may include one or more of SEQ ID NOs: 24-53. In another version of the method, one of the above-described immunogenic compositions is administered to the mammal, and preferably one that comprises virus replicon particles containing one of the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins (or a peptide comprising at least 6 amino acids thereof), or including one of the CTL epitopes set forth in SEQ ID NOs:24-53. In another version of the method, the amino acid sequence of at least one of the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins (or a peptide comprising at least 6 amino acids thereof) is administered to a mammal, such as, for example, a mouse, a guinea pig, a monkey or a human, under such conditions that a protective CTL response is induced in that mammal. In particular, the administered peptides may include one or more of SEQ ID NOs: 24-53.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims, and accompanying drawings where:
In the description that follows, a number of terms used in recombinant DNA, virology and immunology are extensively utilized. In order to provide a clearer and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided.
Filoviruses. The filoviruses (e.g. Ebola Zaire 1976) cause acute hemorrhagic fever characterized by high mortality. Humans can contract filoviruses by infection in endemic regions, by contact with imported primates, and by performing scientific research with the virus. However, there currently are no available vaccines or effective therapeutic treatments for filovirus infection in humans. The virions of filoviruses contain seven proteins: a membrane-anchored glycoprotein (GP), a nucleoprotein (NP), an RNA-dependent RNA polymerase (L), and four virion structural proteins (VP24, VP30, VP35, and VP40). Little is known about the biological functions of these proteins and it is not known which antigens significantly contribute to protection and should therefore be used in an eventual vaccine candidate.
Replicon. A replicon is equivalent to a full-length virus from which all of the viral structural proteins have been deleted. A multiple cloning site can be inserted downstream of the 26S promoter into the site previously occupied by the structural protein genes. Virtually any heterologous gene may be inserted into this cloning site. The RNA that is transcribed from the replicon is capable of replicating and expressing viral proteins in a manner that is similar to that seen with the full-length infectious virus clone. However, in lieu of the viral structural proteins, the heterologous antigen is expressed from the 26S promoter in the replicon. This system does not yield any progeny virus particles because there are no viral structural proteins available to package the RNA into particles.
Particles which appear structurally identical to virus particles can be produced by supplying structural protein RNAs in trans for packaging of the replicon RNA. This is typically done with two defective helper RNAs which encode the structural proteins. One helper consists of a full length infectious clone from which the nonstructural protein genes and the glycoprotein genes are deleted. This helper retains only the terminal nucleotide sequences, the promoter for subgenomic mRNA transcription and the sequences for the viral nucleocapsid protein. The second helper is identical to the first except that the nucleocapsid gene is deleted and only the glycoprotein genes are retained. The helper RNAs are transcribed in vitro and are co-transfected with replicon RNA. Because the replicon RNA retains the sequences for packaging by the nucleocapsid protein, and because the helpers lack these sequences, only the replicon RNA is packaged by the viral structural proteins. The packaged replicon particles are released from the host cell and can then be purified and inoculated into animals. The packaged replicon particles will have a tropism similar to the parent virus. The packaged replicon particles will infect cells and initiate a single round of replication, resulting in the expression of only the virus nonstructural proteins and the product of the heterologous gene that was cloned in the place of the virus structural proteins. In the absence of RNA encoding the virus structural proteins, no progeny virus particles can be produced from the cells infected by packaged replicon particles.
Any alphavirus replicon may be effective in this invention, as long as it has the ability to produce the desired protein or peptide in a manner that induces protective B and T cells in vivo in mammals to which it is administered to (such as, for instance, eastern equine encephalitis, western equine encephalitis, Semlike forest, Sindbis and Venezualen Equine Encephalitis).
The VEE virus replicon (Vrep) is a preferred vector system. The Vrep is a genetically reorganized version of the VEE virus genome in which the structural protein genes are replaced with a gene from an immunogen of interest, such as the Ebola virus virion proteins. This replicon can be transcribed to produce a self-replicating RNA that can be packaged into infectious particles using defective helper RNAs that encode the glycoprotein and capsid proteins of the VEE virus. Since the packaged replicons do not encode the structural proteins, they are incapable of spreading to new cells and therefore undergo a single abortive round of replication in which large amounts of the inserted immunogen are made in the infected cells. The VEE virus replicon system is described in U.S. patent to Johnston et al., U.S. Pat. No. 5,792,462 issued on Aug. 11, 1998.
Subject. Includes both human, animal, e.g., horse, donkey, pig, mouse, hamster, monkey, chicken, and insect such as mosquito.
In one embodiment, the present invention relates to DNA fragments which encode any of the Ebola Zaire 1976 (Mayinga isolate) GP, NP, VP24, VP30, VP35, and VP40 proteins. The GP and NP genes of Ebola Zaire were previously sequenced by Sanchez et al. (1993, supra) and have been deposited in GenBank (accession number L11365). A plasmid encoding the VEE replicon vector containing a unique ClaI site downstream from the 26S promoter was described previously (Davis, N. L. et al., (1996) J. Virol. 70, 3781-3787; Pushko, P. et al. (1997) Virology 239, 389-401). The Ebola GP and NP genes from the Ebola Zaire 1976 virus were derived from PS64- and PGEM3ZF(−)-based plasmids (Sanchez, A. et al. (1989) Virology 170, 81-91; Sanchez, A. et al. (1993) Virus Res. 29, 215-240). From these plasmids, the BamHI-EcoRI (2.3 kb) and BamHI-KpnI (2.4 kb) fragments containing the NP and GP genes, respectively, were subcloned into a shuttle vector that had been digested with BamHI and EcoRI (Davis et al. (1996) supra; Grieder, F. B. et al. (1995) Virology 206, 994-1006). For cloning of the GP gene, overhanging ends produced by KpnI (in the GP fragment) and EcoRI (in the shuttle vector) were made blunt by incubation with T4 DNA polymerase according to methods known in the art. From the shuttle vector, GP or NP genes were subcloned as ClaI-fragments into the ClaI site of the replicon clone, resulting in plasmids encoding the GP or NP genes in place of the VEE structural protein genes downstream from the VEE 26S promoter.
The VP genes of Ebola Zaire were previously sequenced by Sanchez et al. (1993, supra) and have been deposited in GenBank (accession number L11365). The VP genes of Ebola used in the present invention were cloned by reverse transcription of RNA from Ebola-infected Vero E6 cells and subsequent amplification of viral cDNAs using the polymerase chain reaction. First strand synthesis was primed with oligo dT (Life Technologies). Second strand synthesis and subsequent amplification of viral cDNAs were performed with gene-specific primers (SEQ ID NOS:8-16). The primer sequences were derived from the GenBank deposited sequences and were designed to contain a ClaI restriction site for cloning the amplified VP genes into the ClaI site of the replicon vector. The letters and numbers in bold print indicate Ebola gene sequences in the primers and the corresponding location numbers based on the GenBank deposited sequences.
VP24: (1) forward primer is
(SEQ ID NO:8)
5′-GGGATCGATCTCCAGACACCAAGCAAGACC-3′
(10,311-10,331)
(2) reverse primer is
(SEQ ID NO:9)
5′-GGGATCGATGAGTCAGCATATATGAGTTAGCTC-3′
(11,122-11,145)
VP30: (1) forward primer is
SEQ ID NO:10)
5′-CCCATCGATCAGATCTGCGAACCGGTAGAG-3′
(8408-8430)
(2) reverse primer is
(SEQ ID NO:11)
5′-CCCATCGATGTACCCTCATCAGACCATGAGC-3′
(9347-9368)
VP35: (1) forward primer is
(SEQ ID NO:12)
5′-GGGATCGATAGAAAAGCTGGTCTAACAAGATGA-3′
(3110-3133)
(2) reverse primer is
(SEQ ID NO:13)
5′-CCCATCGATCTCACAAGTGTATCATTAATGTAACGT-3′
(4218-4244)
VP40: (1) forward primer is
(SEQ ID NO:14)
5′-CCCATCGATCCTACCTCGGCTGAGAGAGTG-3′
(4408-4428)
(2) reverse primer is
(SEQ ID NO:15)
5′-CCCATCGATATGTTATGCACTATCCCTGAGAAG-3′
(5495-5518)
VP30 #2:
(1) forward primer as for VP30 above
(2) reverse primer is
(SEQ ID NO:16)
5′-CCCATCGATCTGTTAGGGTTGTATCATACC-3′
The Ebola virus genes cloned into the VEE replicon were sequenced. Changes in the DNA sequence relative to the sequence published by Sanchez et al. (1993) are described relative to the nucleotide (nt) sequence number from GenBank (accession number L11365).
The nucleotide sequence we obtained for Ebola virus GP (SEQ ID NO:1) differed from the GenBank sequence by a transition from A to G at nt 8023. This resulted in a change in the amino acid sequence from Ile to Val at position 662 (SEQ ID NO: 17).
The nucleotide sequence we obtained for Ebola virus NP (SEQ ID NO:2) differed from the GenBank sequence at the following 4 positions: insertion of a C residue between nt 973 and 974, deletion of a G residue at nt 979, transition from C to T at nt 1307, and a transversion from A to C at nt 2745. These changes resulted in a change in the protein sequence from Arg to Glu at position 170 and a change from Leu to Phe at position 280 (SEQ ID NO: 18).
The Ebola virus VP24 nucleotide sequence (SEQ ID NO:3) differed from the GenBank sequence at 6 positions, resulting in 3 nonconservative changes in the amino acid sequence. The changes in the DNA sequence of VP24 consisted of a transversion from G to C at nt 10795, a transversion from C to G at nt 10796, a transversion from T to A at nt 10846, a transversion from A to T at nt 10847, a transversion from C to G at nt 11040, and a transversion from C to G at nt 11041. The changes in the amino acid sequence of VP24 consisted of a Cys to Ser change at position 151, a Leu to His change at position 168, and a Pro to Gly change at position 233 (SEQ ID NO: 19).
Two different sequences for the Ebola virus VP30 gene, VP30 and VP30#2 (SEQ ID NOS: 4 and 7) are included. Both of these sequences differ from the GenBank sequence by the insertion of an A residue in the upstream noncoding sequence between nt 8469 and 8470 and an insertion of a T residue between nt 9275 and 9276 that results in a change in the open reading frame of VP30 and VP30#2 after position 255 (SEQ ID NOS: 20 and 23). As a result, the C-terminus of the VP30 protein differs significantly from that previously reported. In addition to these 2 changes, the VP30#2 nucleic acid in SEQ ID NO:7 contains a conservative transition from T to C at nt 9217. Because the primers originally used to clone the VP30 gene into the replicon were designed based on the GenBank sequence, the first clone that we constructed (SEQ ID NO: 4) did not contain what we believe to be the authentic C-terminus of the protein. Therefore, in the absence of the VP30 stop codon, the C-terminal codon was replaced with 37 amino acids derived from the vector sequence. The resulting VP30 construct therefore differed from the GenBank sequence in that it contained 32 amino acids of VP30 sequence (positions 256 to 287, SEQ ID NO:20) and 37 amino acids of irrelevant sequence (positions 288 to 324, SEQ ID NO:20) in the place of the C-terminal 5 amino acids reported in GenBank. However, inclusion of 37 amino acids of vector sequence in place of the C-terminal amino acid (Pro, SEQ ID NO: 23) did not inhibit the ability of the protein to serve as a protective antigen in BALB/c mice. We have also determined that a VEE replicon construct, which contains the authentic C-terminus of VP30 (VP30#2, SEQ ID NO: 23), protects mice against a lethal Ebola challenge.
The nucleotide sequence for Ebola virus VP35 (SEQ ID NO:5) differed from the GenBank sequence by a transition from T to C at nt 4006, a transition from T to C at nt 4025, and an insertion of a T residue between nt 4102 and 4103. These sequence changes resulted in a change from a Ser to a Pro at position 293 and a change from Phe to Ser at position 299 (SEQ ID NO: 21). The insertion of the T residue resulted in a change in the open reading frame of VP35 from that previously reported by Sanchez et al. (1993) following amino acid number 324. As a result, Ebola virus VP35 encodes a protein of 340 amino acids, where amino acids 325 to 340 (SEQ ID NO: 21) differ from and replace the C-terminal 27 amino acids of the previously published sequence.
Sequencing of VP30 and VP35 was also performed on RT/PCR products from RNA derived from cells that were infected with Ebola virus 1976, Ebola virus 1995 or the mouse-adapted Ebola virus. The changes noted above for the Vrep constructs were also found in these Ebola viruses. Thus, we believe that these changes are real events and not artifacts of cloning.
The Ebola virus VP40 nucleotide sequence (SEQ ID NO:6) differed from the GenBank sequence by a transversion from a C to G at nt 4451 and a transition from a G to A at nt 5081. These sequence changes did not alter the protein sequence of VP40 (SEQ ID NO: 22) from that of the published sequence.
Each of the Ebola virus genes were individually inserted into a VEE virus replicon vector. The VP24, VP30, VP35, and VP40 genes of Ebola Zaire 1976 (Mayinga isolate) were cloned by reverse transcription of RNA from Ebola-infected Vero E6 cells and viral cDNAs were amplified using the polymerase chain reaction. The Ebola Zaire 1976 (Mayinga isolate) GP and NP genes were obtained from plasmids already containing these genes (Sanchez, A. et al., (1989) Virology 170, 81-91; Sanchez, A. et al.,(1993) Virus Res. 29, 215-240) and were subcloned into the VEE replicon vector.
After characterization of the Ebola gene products expressed from the VEE replicon constructs in cell culture, these constructs were packaged into infectious VEE virus replicon particles (VRPs) and subcutaneously injected into BALB/c and C57BL/6 mice. As controls in these experiments, mice were also immunized with a VEE replicon expressing Lassa nucleoprotein (NP) as an irrelevant control antigen, or injected with PBS buffer alone. The results of this study demonstrate that VRPs expressing the Ebola GP, NP, VP24, VP30, VP35 or VP40 genes induced protection in mice and may reasonably to expected to provide protection in humans.
DNA or polynucleotide sequences to which the invention also relates include sequences of at least about 6 nucleotides, preferably at least about 8 nucleotides, more preferably at least about 10-12 nucleotides, most preferably at least about 15-20 nucleotides corresponding, i.e., homologous to or complementary to, a region of the Ebola nucleotide sequences described above. Preferably, the sequence of the region from which the polynucleotide is derived is homologous to or complementary to a sequence which is unique to the Ebola genes. Whether or not a sequence is unique to the Ebola gene can be determined by techniques known to those of skill in the art. For example, the sequence can be compared to sequences in databanks, e.g., GenBank and compared by DNA:DNA hybridization. Regions from which typical DNA sequences may be derived include but are not limited to, for example, regions encoding specific epitopes, as well as non-transcribed and/or non-translated regions.
The derived polynucleotide is not necessarily physically derived from the nucleotide sequences shown in SEQ ID NO:1-7, but may be generated in any manner, including for example, chemical synthesis or DNA replication or reverse transcription or transcription, which are based on the information provided by the sequence of bases in the region(s) from which the polynucleotide is derived. In addition, combinations of regions corresponding to that of the designated sequence may be modified in ways known in the art to be consistent with an intended use. The sequences of the present invention can be used in diagnostic assays such as hybridization assays and polymerase chain reaction assays, for example, for the discovery of other Ebola sequences.
In another embodiment, the present invention relates to a recombinant DNA molecule that includes a vector and a DNA sequence as described above. The vector can take the form of a plasmid, a eukaryotic expression vector such as pcDNA3.1, pRcCMV2, pZeoSV2,or pCDM8, which are available from Invitrogen, or a virus vector such as baculovirus vectors, retrovirus vectors or adenovirus vectors, alphavirus vectors, and others known in the art.
In a further embodiment, the present invention relates to host cells stably transformed or transfected with the above-described recombinant DNA constructs. The host cell can be prokaryotic (for example, bacterial), lower eukaryotic (for example, yeast or insect) or higher eukaryotic (for example, all mammals, including but not limited to mouse and human). Both prokaryotic and eukaryotic host cells may be used for expression of the desired coding sequences when appropriate control sequences which are compatible with the designated host are used.
Among prokaryotic hosts, E. coli is the most frequently used host cell for expression. General control sequences for prokaryotes include promoters and ribosome binding sites. Transfer vectors compatible with prokaryotic hosts are commonly derived from a plasmid containing genes conferring ampicillin and tetracycline resistance (for example, pBR322) or from the various pUC vectors, which also contain sequences conferring antibiotic resistance. These antibiotic resistance genes may be used to obtain successful transformants by selection on medium containing the appropriate antibiotics. Please see e.g., Maniatis, Fitsch and Sambrook, Molecular Cloning; A Laboratory Manual (1982) or DNA Cloning, Volumes I and II (D. N. Glover ed. 1985) for general cloning methods. The DNA sequence can be present in the vector operably linked to sequences encoding an IgG molecule, an adjuvant, a carrier, or an agent for aid in purification of Ebola proteins, such as glutathione S-transferase.
In addition, the Ebola virus gene products can also be expressed in eukaryotic host cells such as yeast cells and mammalian cells. Saccharomyces cerevisiae, Saccharomyces carlsbergensis, and Pichia pastoris are the most commonly used yeast hosts. Control sequences for yeast vectors are known in the art. Mammalian cell lines available as hosts for expression of cloned genes are known in the art and include many immortalized cell lines available from the American Type Culture Collection (ATCC), such as CHO cells, Vero cells, baby hamster kidney (BHK) cells and COS cells, to name a few. Suitable promoters are also known in the art and include viral promoters such as that from SV40, Rous sarcoma virus (RSV), adenovirus (ADV), bovine papilloma virus (BPV), and cytomegalovirus (CMV). Mammalian cells may also require terminator sequences, poly A addition sequences, enhancer sequences which increase expression, or sequences which cause amplification of the gene. These sequences are known in the art.
The transformed or transfected host cells can be used as a source of DNA sequences described above. When the recombinant molecule takes the form of an expression system, the transformed or transfected cells can be used as a source of the protein described below.
In another embodiment, the present invention relates to Ebola virion proteins such as
GP having an amino acid sequence corresponding to SEQ ID NO:17 encompassing 676 amino acids,
NP, having an amino acid sequence corresponding to SEQ ID NO:18 encompassing 739 amino acids,
VP24, having an amino acid sequence corresponding to SEQ ID NO:19 encompassing 251 amino acids,
VP30, having an amino acid sequence corresponding SEQ ID NO:20 encompassing 324 amino acids,
VP35, having an amino acid sequence corresponding to SEQ ID NO:21 encompassing 340 amino acids, and
VP40, having an amino acid sequence corresponding to SEQ ID NO:22, encompassing 326 amino acids, and
VP30#2, having an amino acid sequence corresponding to SEQ ID NO:23 encompassing 288 amino acids, or any allelic variation of these amino acid sequences. By allelic variation is meant a natural or synthetic change in one or more amino acids which occurs between different serotypes or strains of Ebola virus and does not affect the antigenic properties of the protein. There are different strains of Ebola (Zaire 1976, Zaire 1995, Reston, Sudan, and Ivory Coast). The NP and VP genes of all these different viruses have not been sequenced. It would be expected that these proteins would have homology among different strains and that vaccination against one Ebola virus strain might afford cross protection to other Ebola virus strains.
A polypeptide or amino acid sequence derived from any of the amino acid sequences in SEQ ID NO:17, 18, 19, 20, 21, 22, and 23 refers to a polypeptide having an amino acid sequence identical to that of a polypeptide encoded in the sequence, or a portion thereof wherein the portion consists of at least 2-5 amino acids, preferably at least 8-10 amino acids, and more preferably at least 11-15 amino acids, or which is immunologically identifiable with a polypeptide encoded in the sequence.
A recombinant or derived polypeptide is not necessarily translated from a designated nucleic acid sequence, or the DNA sequence found in GenBank accession number L11365. It may be generated in any manner, including for example, chemical synthesis, or expression from a recombinant expression system.
When the DNA or RNA sequences described above are in a replicon expression system, such as the VEE replicon described above, the proteins can be expressed in vivo. The DNA sequence for any of the GP, NP, VP24, VP30, VP35, and VP40 virion proteins can be cloned into the multiple cloning site of a replicon such that transcription of the RNA from the replicon yields an infectious RNA encoding the Ebola protein or proteins of interest (see
Use of helper RNAs containing sequences necessary for packaging of the viral replicon transcripts will result in the production of virus-like particles containing replicon RNAs (
In another embodiment, the present invention relates to RNA molecules resulting from the transcription of the constructs described above. The RNA molecules can be prepared by in vitro transcription using methods known in the art and described in the Examples below. Alternatively, the RNA molecules can be produced by transcription of the constructs in vivo, and isolating the RNA. These and other methods for obtaining RNA transcripts of the constructs are known in the art. Please see Current Protocols in Molecular Biology. Frederick M. Ausubel et al. (eds.), John Wiley and Sons, Inc. The RNA molecules can be used, for example, as a direct RNA vaccine, or to transfect cells along with RNA from helper plasmids, one of which expresses VEE glycoproteins and the other VEE capsid proteins, as described above, in order to obtain replicon particles.
In a further embodiment, the present invention relates to a method of producing the recombinant or fusion protein which includes culturing the above-described host cells under conditions such that the DNA fragment is expressed and the recombinant or fusion protein is produced thereby. The recombinant or fusion protein can then be isolated using methodology well known in the art. The recombinant or fusion protein can be used as a vaccine for immunity against infection with Ebola or as a diagnostic tool for detection of Ebola infection.
In another embodiment, the present invention relates to antibodies specific for the above-described recombinant proteins (or polypeptides). For instance, an antibody can be raised against a peptide having the amino acid sequence of any of SEQ ID NO:17-25, or against a portion thereof of at least 10 amino acids, preferably, 11-15 amino acids. Persons with ordinary skill in the art using standard methodology can raise monoclonal and polyclonal antibodies to the protein(or polypeptide) of the present invention, or a unique portion thereof. Materials and methods for producing antibodies are well known in the art (see for example Goding, In Monoclonal Antibodies: Principles and Practice, Chapter 4, 1986).
In another embodiment, the present invention relates to an Ebola vaccine comprising VRPs that express one or more of the Ebola proteins described above. The vaccine is administered to a subject wherein the replicon is able to initiate one round of replication producing the Ebola proteins to which a protective immune response is initiated in said subject.
It is likely that the protection afforded by these genes is due to both the humoral (antibodies (Abs)) and cellular (cytotoxic T cells (CTLs)) arms of the immune system. Protective immunity induced to a specific protein may comprise humoral immunity, cellular immunity, or both. The only Ebola virus protein known to be on the outside of the virion is the GP. The presence of GP on the virion surface makes it a likely target for GP-specific Abs that may bind either extracellular virions or infected cells expressing GP on their surfaces. Serum transfer studies in this invention demonstrate that Abs that recognize GP protect mice against lethal Ebola virus challenge.
In contrast, transfer of Abs specific for NP, VP24, VP30, VP35, or VP40 did not protect mice against lethal Ebola challenge. This data, together with the fact that these are internal virion proteins that are not readily accessible to Abs on either extracellular virions or the surface of infected cells, suggest that the protection induced in mice by these proteins is mediated by CTLs.
CTLs can bind to and lyse virally infected cells. This process begins when the proteins produced by cells are routinely digested into peptides. Some of these peptides are bound by the class I or class II molecules of the major histocompatability complex (MHC), which are then transported to the cell surface. During virus infections, viral proteins produced within infected cells also undergo this process. CTLs that have receptors that bind to both a specific peptide and the MHC molecule holding the peptide lyse the peptide-bearing cell, thereby limiting virus replication. Thus, CTLs are characterized as being specific for a particular peptide and restricted to a class I or class II MHC molecule.
CTLs may be induced against any of the Ebola virus proteins, as all of the viral proteins are produced and digested within the infected cell. Thus, protection to Ebola virus involves CTLs against GP, NP, VP24, VP30, VP35, and/or VP40. It is especially noteworthy that the VP proteins varied in their protective efficacy when tested in genetically inbred mice that differ at the MHC locus. This, together with the inability to demonstrate a role for Abs in protection induced by the VP proteins and the data in Table A below, demonstrates a role for CTLs. Thus, in this invention a vaccine may include several Ebola virus proteins (e.g., at least two), or several CTL epitopes (e.g., at least two), capable of inducing broad protection to different Ebola viruses in outbred populations (e.g. people). To that end, the inventors have identified 18 sequences recognized by CTLs, as determined initially by measuring gamma interferon production by intracellular cytokine staining and gamma interferon secretion by the ELISpot assay. The ability to lyse cells was measured in chromium release assays and protection was evaluated by adoptive transfer of cells into Ebola-naïve mice. Where sequence information is available, the conservation of these CTL epitopes in other Ebola viruses is noted in Table A. Conserved sequences should be capable of inducing protective CTLs to each of the viruses in which the sequence is present.
The identified CTL epitopes are:
Testing to identify the role of CTLs in protection was performed by obtaining CTLs from mice, expanding them in vitro, and transferring the cells into an unvaccinated mouse of the same genetic background. Several hours later, the recipient mice were challenged with 10-1000 pfu of mouse-adapted Ebola virus. They were observed for signs of illness for 28 days. Control animals received no cells or cells that were not specific for Ebola virus. Testing of the cells in vitro indicated that they were CD8+, a marker indicating class I-restriction. The inventors were able to demonstrate that CTLs to these sequences protected at least 80% of recipient mice from challenge. In all of our examples, the ability to lyse peptide-pulsed target cells has predicted protection in mice receiving those cells.
TABLE A
Ebola Virus Epitopes Recognized by Murine CD8 + T cells
% INF-γ
INF-γ
Conserved
Proteina
Epitopeb
ICCc
ELISpotd
51Cre
Protectivef
Restrictiong
Strainsh
GP
WIPYFGPAAEGIYTE (SEQ ID 29)
0.40/0.08
Y
Neg
IP
H-2b
R,G
NP
VYQVNNLEEIC (SEQ ID 24)
1.06/0.11
Y
55.6
Yes
H-2b
G
GQFLFASL (SEQ ID 26)
0.88/0.11
Y
45
Yes
H-2b
S,G
DAVLYYHMM (SEQ ID 27)
0.99/0.11
Y
40.6
Yes
H-2b
G
SFKAALSSL (SEQ ID 28)
0.63/0.04
Y
38.8
Yes
H-2d
VP24
NILKFINKLDALHVV (SEQ ID 25)
0.52/0.09
Y
45.9
Yes
H-2d
G
NYNGLLSSIEGTQN (SEQ ID 30)
0.38/0.09
Y
50.6
Yes
H-2d
R,G
RMKPGPAKFSLLHESTLKAFTQGSS
3.34/0.09
Y
43.2
Yes*
H-2d
R,G
(SEQ ID 31)
VP30
FSKSQLSLLCETHLR (SEQ ID 32)
0.45/0.15
N
47.3
Yes*
H-2b
DLQSLIMFITAFLNI (SEQ ID 33)
0.7/0.15
N
ND
Yes*
H-2b
VP35
RNIMYDHL (SEQ ID 34)
1.53/0.22
Y
87.4
Yes
H-2b
MVAKYDLL (SEQ ID 35)
1.63/0.22
N
78.9
Yes
H-2b
R
CDIENNPGL (SEQ ID 36)
1.99/0.15
N
80.4
Yes
H-2b
VP40
AFLQEFVLPPVQLPQ (SEQ ID 37)
0.45/0.22
ND
ND
IP
H-2d
FVLPPVQLPQYFTFDLTALK (SEQ ID 38)
0.41/0.22
ND
38
Yes*
H-2d
KSGKKGNSADLTSPEKIQAIMTSLQDFKIV
0.6/0.22
N
36.4
IP
H-2d
(SEQ ID 39)
PLRLLRIGNQAFLQE (SEQ ID 40)
0.7/0.05
N
52.8
Yes
H-2b
RIGNQAFLQEFVLPP (SEQ ID 41)
0.38/0.05
N
46.7
IP
H-2b
aProteins are from Ebola Zaire '76 virus: GP, glycoprotein, NP, nucleoprotein, or the virion proteins VP24, VP30, VP35 or VP40.
bEpitope, indicates peptide sequence(s) tested in the T cell assays. Underlined regions are presumed minimum epitopes based on binding motifs, algorithm predictions and/or demonstrated effects based on synthesis of shorter peptides.
cICC data is % of CD8 that are INF-γ positive and CD8 positive/background
dIFN-γ ELISpot assays indicated (Y, yes; N, no) presence of secreted interferon-γ.
e51Cr data is specific lysis at the 25:1 E:T ratio.
fProtection observed in 100% of naive mice receiving CTLs specific for the designated epitopes, except where marked with *, in which cases protection of 80–90% was observed. IP, in progress (data within 2 weeks).
gRestriction indicates the major histocompatability type for which lysis was observed. H-2b mice are C57B1/6 and H-2dare Balb/c.
hConserved strains: underlined sequences representing epitopes are identical in Sudan, Gabon and Reston Ebola viruses as indicated by S, G or R, respectively.
ND, not determined
In another embodiment, the invention relates to a vaccine against Ebola infection including at least one of these CTL epitope sequences, and preferably at least one CTL epitope having the amino acid sequence of SEQ ID NOs:24-53. Preferably, the vaccine includes at least two of the CTL epitope sequences, more preferably at least three, more preferably at least four, more preferably at least five, and more preferably all of the sequences. As shown in the examples below, protection is increased as the number of CTL epitopes in the immunogenic composition or vaccine is increased, and also as the number of epitopes from different Ebola proteins is increased.
In another embodiment, the vaccine includes a CTL epitope sequence from at least two different proteins selected from the group consisting of GP, NP, VP24, VP30, VP35 and VP40. More preferably, the vaccine includes a CTL epitope sequence from at least three different proteins from that group, more preferably at least four, more preferably at least five, and most preferably includes at least one CTL epitope sequence from each of the six proteins. The CTL epitopes may have the amino acid sequences as set forth in SEQ ID NOs:24-53. It is noted that administering the GP peptide alone may prevent the induction of protective antibodies, which may be undesirable.
In a further vaccine embodiment, the vaccine comprises virus replicon particles (preferably VEE virus replicon particles but other alphavirus replicon particles will do as described above) expressing the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 proteins, or any combination of different VEE virus replicons each expressing one or more different Ebola proteins selected from GP, NP, VP24, VP30, VP35 and VP40. For instance, in a preferred embodiment the Ebola VRPs express one or more of the peptides specified by SEQ ID NOs: 24-53.
In another vaccine embodiment, the vaccine may include at a minimum at least one of the Ebola proteins selected from GP, NP, VP24, VP30, VP35 and VP40, but preferably contains at least two, more preferably at least three, more preferably at least four, more preferably at least five, and most preferably all of them. It is noted again that administering the GP peptide alone may prevent the induction of protective antibodies, which may be undesirable. For instance, in a preferred embodiment the vaccine includes at least the VP30, VP35 and VP40 proteins. In another preferred embodiment, the vaccine may include one or more of SEQ ID NOs: 24-53.
When considering which type of vaccine may be most effective for an individual, it is noted that the same protective response could be induced by the peptide or the full protein produced from the VRPs. Production of the peptide intracellularly is generally preferred because it is usually (but not always) more effective than providing it extracellularly. Thus, vaccines containing VRPs may be preferred because the VRPs infect cells and therefore achieve intracellular production.
Such vaccines might be delivered as synthetic peptides, or as fusion proteins, alone or co-administered with cytokines and/or adjuvants or carriers safe for human use, e.g. aluminum hydroxide, to increase immunogenicity. In addition, sequences such as ubiquitin can be added to increase antigen processing for more effective CTL responses.
In yet another embodiment, the present invention relates to a method for providing immunity against Ebola virus, said method comprising administering one or more VRPs expressing any combination of the GP, NP, VP24, VP30 or VP30#2, VP35 and VP40 Ebola proteins to a subject such that a protective immune reaction is generated. In another related embodiment, the method may entail administering one or more VRPs expressing any combination of the peptides designated SEQ ID NOs:24-53, or simply one or more of the peptides designated SEQ ID NOs:24-53.
Vaccine formulations of the present invention comprise an immunogenic amount of a VRP, such as for example EboVP24VRP described above, or, for a multivalent vaccine, a combination of replicons, in a pharmaceutically acceptable carrier. An “immunogenic amount” is an amount of the VRP(s) sufficient to evoke an immune response in the subject to which the vaccine is administered. An amount of from about 104-108 focus-forming units per dose is suitable, depending upon the age and species of the subject being treated. The subject may be inoculated 2-3 times. Exemplary pharmaceutically acceptable carriers include, but are not limited to, sterile pyrogen-free water and sterile pyrogen-free physiological saline solution.
Administration of the VRPs disclosed herein may be carried out by any suitable means, including parenteral injection (such as intraperitoneal, subcutaneous, or intramuscular injection), in ovo injection of birds, orally, or by topical application of the virus (typically carried in a pharmaceutical formulation) to an airway surface. Topical application of the virus to an airway surface can be carried out by intranasal administration (e.g., by use of dropper, swab, or inhaler which deposits a pharmaceutical formulation intranasally). Topical application of the virus to an airway surface can also be carried out by inhalation administration, such as by creating respirable particles of a pharmaceutical formulation (including both solid particles and liquid particles) containing the replicon as an aerosol suspension, and then causing the subject to inhale the respirable particles. Methods and apparatus for administering respirable particles of pharmaceutical formulations are well known, and any conventional technique can be employed. Oral administration may be in the form of an ingestable liquid or solid formulation.
When the replicon RNA or DNA is used as a vaccine, the replicon RNA or DNA can be administered directly using techniques such as delivery on gold beads (gene gun), delivery by liposomes, or direct injection, among other methods known to people in the art. Any one or more DNA constructs or replicating RNA described above can be use in any combination effective to elicit an immunogenic response in a subject. Generally, the nucleic acid vaccine administered may be in an amount of about 1-5 ug of nucleic acid per dose and will depend on the subject to be treated, capacity of the subject's immune system to develop the desired immune response, and the degree of protection desired. Precise amounts of the vaccine to be administered may depend on the judgement of the practitioner and may be peculiar to each subject and antigen.
The vaccine may be given in a single dose schedule, or preferably a multiple dose schedule in which a primary course of vaccination may be with 1-10 separate doses, followed by other doses given at subsequent time intervals required to maintain and or reinforce the immune response, for example, at 1-4 months for a second dose, and if needed, a subsequent dose(s) after several months. Examples of suitable immunization schedules include: (i) 0, 1 months and 6 months, (ii) 0, 7 days and 1 month, (iii) 0 and 1 month, (iv) 0 and 6 months, (v) 0, 1 and 2 months, or other schedules sufficient to elicit the desired immune responses expected to confer protective immunity, or reduce disease symptoms, or reduce severity of disease.
In a further embodiment, the present invention relates to a method of detecting the presence of antibodies against Ebola virus in a sample. Using standard methodology well known in the art, a diagnostic assay can be constructed by coating on a surface (i.e. a solid support for example, a microtitration plate, a membrane (e.g. nitrocellulose membrane) or a dipstick), all or a unique portion of any of the Ebola proteins described above or any combination thereof, and contacting it with the serum of a person or animal suspected of having Ebola. The presence of a resulting complex formed between the Ebola protein(s) and serum antibodies specific therefor can be detected by any of the known methods common in the art, such as fluorescent antibody spectroscopy or colorimetry. This method of detection can be used, for example, for the diagnosis of Ebola infection and for determining the degree to which an individual has developed virus-specific antibodies after administration of a vaccine.
In yet another embodiment, the present invention relates to a method for detecting the presence of Ebola virion proteins in a sample. Antibodies against GP, NP, and the VP proteins could be used for diagnostic assays. Using standard methodology well known in the art, a diagnostics assay can be constructed by coating on a surface (i.e. a solid support, for example, a microtitration plate or a membrane (e.g. nitrocellulose membrane)), antibodies specific for any of the Ebola proteins described above, and contacting it with serum or a tissue sample of a person suspected of having Ebola infection. The presence of a resulting complex formed between the protein or proteins in the serum and antibodies specific therefor can be detected by any of the known methods common in the art, such as fluorescent antibody spectroscopy or colorimetry. This method of detection can be used, for example, for the diagnosis of Ebola virus infection.
In another embodiment, the present invention relates to a diagnostic kit which contains any combination of the Ebola proteins described above and ancillary reagents that are well known in the art and that are suitable for use in detecting the presence of antibodies to Ebola in serum or a tissue sample. Tissue samples contemplated can be from monkeys, humans, or other mammals.
In yet another embodiment, the present invention relates to DNA or nucleotide sequences for use in detecting the presence of Ebola virus using the reverse transcription-polymerase chain reaction (RT-PCR). The DNA sequence of the present invention can be used to design primers which specifically bind to the viral RNA for the purpose of detecting the presence of Ebola virus or for measuring the amount of Ebola virus in a sample. The primers can be any length ranging from 7 to 400 nucleotides, preferably at least 10 to 15 nucleotides, or more preferably 18 to 40 nucleotides. Reagents and controls necessary for PCR reactions are well known in the art. The amplified products can then be analyzed for the presence of viral sequences, for example by gel fractionation, with or without hybridization, by radiochemistry, and immunochemistry techniques.
In yet another embodiment, the present invention relates to a diagnostic kit which contains PCR primers specific for Ebola virus and ancillary reagents for use in detecting the presence or absence of Ebola in a sample using PCR. Samples contemplated can be obtained from human, animal, e.g., horse, donkey, pig, mouse, hamster, monkey, or other mammals, birds, and insects, such as mosquitoes.
The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors and thought to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
The following MATERIALS AND METHODS were used in the examples that follow.
Cells Lines and Viruses
BHK (ATCC CCL 10), Vero 76 (ATCC CRL 1587), and Vero E6 (ATCC CRL 1586) cell lines were maintained in minimal essential medium with Earle's salts, 5-10% fetal bovine serum, and 50 □g/mL gentamicin sulfate. For CTL assays, EL4 (ATCC TIB39), L5178Y (ATCC CRL 1723) and P815 (ATCC TIB64) were maintained in Dulbecco's minimal essential medium supplemented with 5-10% fetal bovine serum and antibiotics.
A stock of the Zaire strain of Ebola virus originally isolated from a patient in the 1976 outbreak (Mayinga) and passaged intracerebrally 3 times in suckling mice and 2 times in Vero cells was adapted to adult mice through serial passage in progressively older suckling mice (Bray et al.,(1998) J. Infect. Dis. 178, 651-661). A plaque-purified ninth-mouse-passage isolate which was uniformly lethal for adult mice (“mouse-adapted virus”) was propagated in Vero E6 cells, aliquotted, and used in all mouse challenge experiments and neutralization assays.
A stock of the Zaire strain of Ebola 1976 virus was passaged spleen to spleen in strain 13 guinea pigs four times. This guinea pig-adapted strain was used to challenge guinea pigs.
Construction and Packaging of Recombinant VEE Virus Replicons (VRPs)
Replicon RNAs were packaged into VRPs as described (Pushko et al., 1997, supra). Briefly, capped replicon RNAs were produced in vitro by T7 run-off transcription of NotI-digested plasmid templates using the RiboMAX T7 RNA polymerase kit (Promega). BHK cells were co-transfected with the replicon RNAs and the 2 helper RNAs expressing the structural proteins of the VEE virus. The cell culture supernatants were harvested approximately 30 hours after transfection and the replicon particles were concentrated and purified by centrifugation through a 20% sucrose cushion. The pellets containing the packaged replicon particles were suspended in PBS and the titers were determined by infecting Vero cells with serial dilutions of the replicon particles and enumerating the infected cells by indirect immunofluorescence with antibodies specific for the Ebola proteins.
Immunoprecipitation of Ebola Virus Proteins Expressed from VEE Virus Replicons
BHK cells were transfected with either the Ebola virus GP, NP, VP24, VP30, VP35, or VP40 replicon RNAs. At 24 h post-transfection, the culture medium was replaced with minimal medium lacking cysteine and methionine, and proteins were labeled for 1 h with 35S-labeled methionine and cysteine. Cell lysates or supernatants (supe) were collected and immunoprecipitated with polyclonal rabbit anti-Ebola virus serum bound to protein A beads. 35S-labeled Ebola virus structural proteins from virions grown in Vero E6 cells were also immunoprecipitated as a control for each of the virion proteins. Immunoprecipitated proteins were resolved by electrophoresis on an 11% SDS-polyacrylamide gel and were visualized by autoradiography.
Vaccination of Mice with VEE Virus Replicons
Groups of 10 BALB/c or C57BL/6 mice per experiment were subcutaneously injected at the base of the neck with 2×106 focus-forming units of VRPs encoding the Ebola virus genes. As controls, mice were also injected with either a control VRP encoding the Lassa nucleoprotein (NP) or with PBS. For booster inoculations, animals received identical injections at 1 month intervals. Data are recorded as the combined results of 2 or 3 separate experiments.
Ebola Infection of Mice
One month after the final booster inoculation, mice were transferred to a BSL-4 containment area and challenged by intraperitoneal (ip) inoculation of 10 plaque-forming units (pfu) of mouse-adapted Ebola virus (approximately 300 times the dose lethal for 50% of adult mice). The mice were observed daily, and morbidity and mortality were recorded. Animals surviving at day 21 post-infection were injected again with the same dose of virus and observed for another 21 days.
In some experiments, 4 or 5 mice from vaccinated and control groups were anesthetized and exsanguinated on day 4 (BALB/c mice) or day 5 (C57BL/6 mice) following the initial viral challenge. The viral titers in individual sera were determined by plaque assay.
Passive Transfer of Immune Sera to Naive Mice.
Donor sera were obtained 28 days after the third inoculation with 2×106 focus-forming units of VRPs encoding the indicated Ebola virus gene, the control Lassa NP gene, or from unvaccinated control mice. One mL of pooled donor sera was administered intraperitoneally (ip) to naive, syngeneic mice 24 h prior to intraperitoneal challenge with 10 pfu of mouse-adapted Ebola virus.
Vaccination and Challenge of Guinea Pigs.
EboGPVRP or EboNPVRP (1×107 focus-forming units in 0.5 ml PBS) were administered subcutaneously to inbred strain 2 or strain 13 guinea pigs (300-400 g). Groups of five guinea pigs were inoculated on days 0 and 28 at one (strain 2) or two (strain 13) dorsal sites. Strain 13 guinea pigs were also boosted on day 126. One group of Strain 13 guinea pigs was vaccinated with both the GP and NP constructs. Blood samples were obtained after vaccination and after viral challenge. Guinea pigs were challenged on day 56 (strain 2) or day 160 (strain 13) by subcutaneous administration of 1000 LD50 (1×104 PFU) of guinea pig-adapted Ebola virus. Animals were observed daily for 60 days, and morbidity (determined as changes in behavior, appearance, and weight) and survival were recorded. Blood samples were taken on the days indicated after challenge and viremia levels were determined by plaque assay.
Virus Titration and Neutralization Assay.
Viral stocks were serially diluted in growth medium, adsorbed onto confluent Vero E6 cells in 6- or 12-well dishes, incubated for 1 hour at 37° C., and covered with an agarose overlay (Moe, J. et al. (1981) J. Clin. Microbiol. 13:791-793). A second overlay containing 5% neutral red solution in PBS or agarose was added 6 days later, and plaques were counted the following day. Pooled pre-challenge serum samples from some of the immunized groups were tested for the presence of Ebola-neutralizing antibodies by plaque reduction neutralization assay. Aliquots of Ebola virus in growth medium were mixed with serial dilutions of test serum, or with normal serum, or medium only, incubated at 37° C. for 1 h, and used to infect Vero E6 cells. Plaques were counted 1 week later.
Cytotoxic T Cell Assays.
BALB/c and C57BL/6 mice were inoculated with VRPs encoding Ebola virus NP or VP24 or the control Lassa NP protein. Mice were euthanized at various times after the last inoculation and their spleens removed. The spleens were gently ruptured to generate single cell suspensions. Spleen cells (1×106/ml) were cultured in vitro for 2 days in the presence of 10-25 □M of peptides synthesized from Ebola virus NP or VP24 amino acid sequences, and then for an additional 5 days in the presence of peptide and 10% supernatant from concanavalin A-stimulated syngeneic spleen cells. Synthetic peptides were made from Ebola virus amino acid sequences predicted by a computer algorithm (HLA Peptide Binding Predictions, Parker, K. C., et al. (1994) J. Immunol. 152:163) to have a likelihood of meeting the MHC class I binding requirements of the BALB/c (H-2d) and C57BL/6 (H-2b) haplotypes. Only 2 of 8 peptides predicted by the algorithm and tested to date have been identified as containing CTL epitopes. After in vitro restimulation, the spleen cells were tested in a standard 51chromium-release assay well known in the art (see, for example, Hart et al. (1991) Proc. Natl. Acad. Sci. USA 88: 9449-9452). Percent specific lysis of peptide-coated, MHC-matched or mismatched target cells was calculated as:
Spontaneous cpm are the number of counts released from target cells incubated in medium. Maximum cpm are obtained by lysing target cells with 1% Triton X-100. Experimental cpm are the counts from wells in which target cells are incubated with varying numbers of effector (CTL) cells. Target cells tested were L5178Y lymphoma or P815 mastocytoma cells (MHC matched to the H2d BALB/c mice and EL4 lymphoma cells (MHC matched to the H2b C57BL/6 mice). The effector:target (E:T) ratios tested were 25:1, 12:1, 6:1 and 3:1.
Survival of Mice Inoculated with VRPs Encoding Ebola Proteins
Mice were inoculated two or three times at 1 month intervals with 2×106 focus-forming units of VRPs encoding individual Ebola virus genes, or Lassa virus NP as a control, or with phosphate buffered saline (PBS). Mice were challenged with 10 pfu of mouse-adapted Ebola virus one month after the final immunization. The mice were observed daily, and morbidity and mortality data are shown in Table 1A for BALB/c mice and Table 1B for C57BL/6 mice. The viral titers in individual sera of some mice on day 4 (BALB/c mice) or day 5 (C57BL/6 mice) following the initial viral challenge were determined by plaque assay.
TABLE 1
Survival Of Mice Inoculated With VRPs Encoding Ebola Proteins
VRP
#Injections
S/T1 (%)
MDD2
V/T3
Viremia4
A. BALB/c Mice
EboNP
3
30/30 (100%)
5/5
5.2
2
19/20 (95%)
7
5/5
4.6
EboGP
3
15/29 (52%)
8
1/5
6.6
2
14/20 (70%)
7
3/5
3.1
EboVP24
3
27/30 (90%)
8
5/5
5.2
2
19/20 (95%)
6
4/4
4.8
EboVP30
3
17/20 (85%)
7
5/5
6.2
2
11/20 (55%)
7
5/5
6.5
EboVP35
3
5/19 (26%)
7
5/5
6.9
2
4/20 (20%)
7
5/5
6.5
EboVP40
3
14/20 (70%)
8
5/5
4.6
2
17/20 (85%)
7
5/5
5.6
LassaNP
3
0/29 (0%)
7
5/5
8.0
2
0/20 (0%)
7
5/5
8.4
none(PBS)
3
1/30 (3%)
6
5/5
8.3
2
0/20 (0%)
6
5/5
8.7
B. C57BL/6 Mice
EboNP
3
15/20 (75%)
8
5/5
4.1
2
8/10 (80%)
9
ND5
ND
EboGP
3
19/20 (95%)
10
0/5
—
2
10/10 (100%)
—
ND
ND
EboVP24
3
0/20 (0%)
7
5/5
8.6
EboVP30
3
2/20 (10%)
8
5/5
7.7
EboVP35
3
14/20 (70%)
8
5/5
4.5
EboVP40
3
1/20 (5%)
7
4/4
7.8
LassaNP
3
1/20 (5%)
7
4/4
8.6
2
0/10 (0%)
7
ND
ND
none(PBS)
3
3/20 (15%)
7
5/5
8.6
2
0/10 (0%)
7
ND
ND
1S/T, Survivors/total challenged.
2MDD, Mean day to death
3V/T, Number of mice with viremia/total number tested.
4Geometric mean of Log10 viremia titers in PFU/mL. Standard errors for all groups were 1.5 or less, except for the group of BALB/c mice given 2 inoculations of EboGP, which was 2.2.
5ND, not determined.
VP24-Immunized BALB/c Mice Survive a High-Dose Challenge with Ebola Virus
BALB/c mice were inoculated two times with 2×106 focus-forming units of EboVP24VRP. Mice were challenged with either 1×103 pfu or 1×105 pfu of mouse-adapted Ebola virus 1 month after the second inoculation. Morbidity and mortality data for these mice are shown in Table 2.
TABLE 2
VP24-Immunized BALB/c Mice Survive A High-Dose Challenge
With Ebola virus
Replicon
Challenge Dose
Survivors/Total
EboVP24
1 × 103 pfu
5/5
(3 × 104 LD50)
EboVP24
1 × 105 pfu
5/5
(3 × 106 LD50)
None
1 × 103 pfu
0/4
(3 × 104 LD50)
None
1 × 105 pfu
0/3
(3 × 106 LD50)
Passive Transfer of Immune Sera Can Protect Naive Mice from a Lethal Challenge of Ebola Virus
Donor sera were obtained 28 days after the third inoculation with 2×106 focus-forming units of VRPs encoding the indicated Ebola virus gene, the control Lassa NP gene, or from unvaccinated control mice. One mL of pooled donor sera was administered intraperitoneally (ip) to naive, syngeneic mice 24 h prior to intraperitoneal challenge with 10 pfu of mouse-adapted Ebola virus.
TABLE 3
Passive Transfer of Immune Sera Can Protect Unvaccinated Mice
from a Lethal Challenge of Ebola Virus
Specificity of
Survivors/
Mean Day
Donor Sera
Total
of Death
A. BALB/c Mice
Ebola GP
15/20
8
Ebola NP
1/20
7
Ebola VP24
0/20
6
Ebola VP30
0/20
7
Ebola VP35
ND1
ND
Ebola VP40
0/20
6
Lassa NP
0/20
7
Normal mouse sera
0/20
6
B. C57BL/6 Mice
Ebola GP
17/20
7
Ebola NP
0/20
7
Ebola VP24
ND
ND
Ebola VP30
ND
ND
Ebola VP35
0/20
7
Ebola VP40
ND
ND
Lassa NP
0/20
7
Normal mouse sera
O/20
7
1ND, not determined
Immunogenicity and Efficacy of VRepEboGP and VRepEboNP in Guinea Pigs.
EboGPVRP or EboNPVRP (1×107 IU in 0.5 ml PBS) were administered subcutaneously to inbred strain 2 or strain 13 guinea pigs (300-400 g). Groups of five guinea pigs were inoculated on days 0 and 28 at one (strain 2) or two (strain 13) dorsal sites. Strain 13 guinea pigs were also boosted on day 126. One group of Strain 13 guinea pigs was vaccinated with both the GP and NP constructs. Blood samples were obtained after vaccination and after viral challenge.
Sera from vaccinated animals were assayed for antibodies to Ebola by plaque-reduction neutralization, and ELISA. Vaccination with VRepEboGP or NP induced high titers of antibodies to the Ebola proteins (Table 4) in both guinea pig strains. Neutralizing antibody responses were only detected in animals vaccinated with the GP construct (Table 4).
Guinea pigs were challenged on day 56 (strain 2) or day 160 (strain 13) by subcutaneous administration of 1000 LD50 (104 PFU) of guinea pig-adapted Ebola virus. Animals were observed daily for 60 days, and morbidity (determined as changes in behavior, appearance, and weight) and survival were recorded. Blood samples were taken on the days indicated after challenge and viremia levels were determined by plaque assay. Strain 13 guinea pigs vaccinated with the GP construct, alone or in combination with NP, survived lethal Ebola challenge (Table 4). Likewise, vaccination of strain 2 inbred guinea pigs with the GP construct protected 3/5 animals against death from lethal Ebola challenge, and significantly prolonged the mean day of death (MDD) in one of the two animals that died (Table 4). Vaccination with NP alone did not protect either guinea pig strain.
TABLE 4
Immunogenicity and efficacy of VRepEboGP and VRepEboNP in
guinea pigs
Survivors/
Viremiac
VRP
ELISAa
PRNT50
total(MDDb)
d7
d14
A. Strain 2 guinea pigs
GP
4.1
30
3/5 (13 + 2.8)
2.3
1.8
NP
3.9
<10
0/5 (9.2 + 1.1)
3.0
—
Mock
<1.5
<10
0/5 (8.8 + 0.5)
3.9
—
B. Strain 13 guinea pigs
GP
4.0
140
5/5
<2.0
<2.0
GP/NP
3.8
70
5/5
<2.0
<2.0
NP
2.8
<10
1/5 (8.3 + 2.2)
4.6
—
Lassa NP
<1.5
<10
2/5 (8.3 + 0.6)
4.8
—
aData are expressed as geometric mean titers, log10.
bMDD, mean day to death
cGeometric mean of log10 viremia titers in PFU/mL. Standard errors for all groups were 0.9 or less.
Induction of Murine CTL Responses to Ebola Virus NP and Ebola Virus VP24 Proteins
BALB/c and C57BL/6 mice were inoculated with VRPs encoding Ebola virus NP or VP24. Mice were euthanized at various times after the last inoculation and their spleens removed. Spleen cells (1×106/ml) were cultured in vitro for 2 days in the presence of 10 to 25 □M of peptides, and then for an additional 5 days in the presence of peptide and 10% supernatant from concanavalin A-stimulated syngeneic spleen cells. After in vitro restimulation, the spleen cells were tested in a standard 51chromium-release assay. Percent specific lysis of peptide-coated, MHC-matched or mismatched target cells was calculated as:
In the experiments shown, spontaneous release did not exceed 15%.
TABLE 5
Induction of murine CTL responses to Ebola virus NP and Ebola
virus VP24 proteins.
% Specific Lysis
E:T ratio
Mice, VRP1
Peptide2
Cell3
25
BALB/c, VP24
None
P815
55
BALB/c, VP24
SEQ ID NO: 25
P815
93
C57BL/6, EboNP
None
EL4
2
C57BL/6, EboNP4
SEQ ID NO: 24
EL4
70
C57BL/6, EboNP
LassaNP
EL4
2
C57BL/6, LassaNP
None
L5178Y
1
C57BL/6, LassaNP
SEQ ID NO: 24
L5178Y
0
C57BL/6, LassaNP
None
EL4
2
C57BL/6, LassaNP
SEQ ID NO: 24
EL4
6
1Indicates the mouse strain used and the VRP used as the in vivo immunogen. In vitro restimulation was performed using SEQ ID NO: 24 peptide for BALB/c mice and SEQ ID NO: 23 for all C57BL/6 mice shown.
2Indicates the peptide used to coat the target cells for the chromium release assay.
3Target cells are MHC-matched to the effector cells, except for the L5178Y cells that are C57BL/6 mismatched.
4High levels of specific lysis (>40%) were also observed using E:T ratios of 12, 6, 3, or 1:1.
Induction of Murine T Cell Responses that Protect Against Ebola Challenge
Mice and injections. BALB/c and C57Bl/6 mice were injected sc with 2×106 IU of VEE virus replicons encoding either the individual Ebola genes or Lassa NP (3 injections 1 month apart). The genes used to make replicons are from the human Zaire76 virus. One month after the final immunization, mice were transferred to BSL-4 containment and challenged by ip inoculation of 10 or 1000 pfu (300 or 30000 LD50) of mouse-adapted Ebola Zaire. This virus has amino acid changes in NP at nt 683 (S to G), VP35 at nt 3163 (A to V), VP24 at nt 10493 (T to I), and in L at nt 14380 (F to L) and nt 16174 (I to V). There are three other nt changes, including an insertion in the intergenic region at nt 10343. GenBank accession number AF499101.
T cell assays. Single cell suspensions were prepared from spleens by passage through cell 70 μM strainers. Spleen cells were depleted of erythrocytes by treatment with buffered ammonium chloride solution and enumerated by trypan blue exclusion on a hemacytometer. For in vitro restimulations, 1-5 μg peptide(s) and human recombinant IL-2 (10 U/ml, National Cancer Institute) were added to a cell density of 1×106/ml and the cultures incubated 4-7 days. For intracellular IFN-γ staining, splenocytes were cultured at 37° C. for 5 hr with 1-5 μg of peptide(s) or PMA (25 ng/ml) and ionomycin (1.25 ug/ml) in 100 μl complete medium containing 10 μg/ml brefeldin A (BFA). After culture, the cells were blocked with mAbs to FcRIII/II receptor and stained with αCD44 FITC and anti-CD8 Cychrome (Pharmingen, San Diego, Calif.) in PBS/BFA. The cells were then fixed in 1% formaldehyde (Ted Pella, Redding, Calif.), permeabilized with PBS containing 0.5% saponin, and stained with αIFN-γ PE (Pharmingen, San Diego, Calif.). The data were acquired using a FACSCalibur flow cytometer and analyzed with CELLQuest software (Becton-Dickinson. Cytotoxicity assays were performed using target cells (EL4, L5178Y) labeled with 51Cr (Na2CrO4; New England Nuclear, Boston, Mass.) and pulsed with peptide for 1.5 hours. Unpulsed target cells were used as negative controls. Various numbers of effector cells were incubated with 2500 target cells for 4 hours. Percentage specific release was calculated as: % specific release=(experimental−spontaneous)/(maximum−spontaneous)×100. Spontaneous release values were obtained by incubation of target cells in medium alone and were routinely <10% of maximum release. Maximum release values were obtained by the addition of 100 μl 1% TritonX-100.
Adoptive transfer experiments. After in vitro restimulation, cells are Ficoll purified, washed three times with 0.3M methyl-a-D-mannopyranoside and twice with complete media. Cells are counted and adjusted to 25.0×10^6 cells/ml in endotoxin-free PBS. A total volume of 0.2 mls is given to each mouse by i.p. injection 4 hr before challenge with 1000 PFU of mouse-adapted Ebola virus. Animals are observed and sickness or death is noted on daily charts.
As shown in Table A, this data identifies the protective mechanism induced by VRP vaccination, showing the role of T cells. It indicates the ability to predict protection from in vitro assays, specifically the intracellular cytokine and chromium release assays. Thus, a positive ICC result is reasonably predictive of conferred protection, even if the protection is listed as incomplete; the rest of the data strongly indicate protection. Notably, where the CTL sequences are conserved between Zaire and the other Ebola viruses, cross-protection may reasonably be inferred. (The protection in Table A refers to adoptive transfer of CTLs to unvaccinated mice before challenge, not the vaccination with a certain protein.)
Determination of Interference in Protection by Multiple Replicons
The purpose of this experiment was to determine if multiple VEE replicons that do not provide complete protection (VP24, 30, 40 in BL/6 mice) will interfere with a protective replicon Ebola NP that has defined CTL epitopes. Co-administration did not interfere with the induction of protection.
Vaccine
Survival
VRep EBOV NP, VP24, VP30, VP40
10/10
VRep EBOV NP
6/6
PBS
0/7
The CTLs to NP are CD8(+),and recognize epitopes SEQ ID NO:24, 26 and 27. Evaluation of the ability to lyse peptide-pulsed target cells was assessed using spleen cells from mice vaccinated with the EBOC VRepNP alone, or all four replicons (NP, VP24, VP30 and VP40). Although responses were somewhat lower in the mice receiving four replicons, the threshold of immunity was maintained.
% Lysis of target cells coated
with peptide (background on
untreated target cells is subtracted)
Vaccine
Effector/target ratio
NP-1
NP-8
NP-17
NP
100:1
55
31
64
50:1
61
23
45
25:1
67
15
31
12:1
51
13
21
Mix
100:1
41
40
45
50:1
37
32
28
25:1
26
33
19
12:1
19
18
12
Improved Efficacy Induced by a Cocktail Formulation of Suboptimal EBOV Vrep
In studies where we examined the protective efficacy of replicons individually, we observed that some replicons (such as VP30, VP24 and VP40) protected fewer than 100% of the mice. When protection was less than 50%, we suggested that the protein was not particularly protective for that mouse strain. However, in some cases, we did observe that 20-30% of the mice survived, suggesting that we might be able to optimize our vaccine strategy to provide protection with those proteins. As we are evaluating a cocktail formulation, we approached this issue by injecting mice with combinations of the three VP replicons than had poor efficacy in C57Bl/6 mice.
C57BL/6 mice were injected SC at the base of the neck with 2.0×106 packaged VEE virus replicon particles for each Ebola VP protein, then rested for 27 days and then boosted twice at days 28 and 56. On day 84, mice were injected intraperitoneally with approximately 3×104 LD50 (1000 PFU) of mouse-adapted Ebola virus.
Strain
Vaccine
Survival
C57BL/6
VRep VP35
30/30
C57BL/6
VReps VP35, VP30, VP24, VP40
30/30
C57BL/6
Medium
0/23
C57BL/6
VReps VP30, VP24, VP40
28/30
The data indicate that combining the three VP replicons provided significantly better protection than when we administered them singly. Of note, the VP24 replicon has never protected a single C57BL/6 mouse when administered alone and is not likely contributing to protection. However, importantly, its inclusion in the formulation also does not interfere with induction of protective responses to the other VPs.
These data shows that a cocktail formulation may be a preferred vaccine because it induces a broader array of T cells (i.e. CTLs to multiple proteins) and that, together, these may meet the threshold needed for protection. We expect the same phenomenon will apply to non-human primate studies. This also provides support for the inclusion of multiple Ebola peptides/proteins in a cocktail formulation. As an example, if a human infected with Ebola needs 1 million effectors, but vaccination induces only 400,000 to each protein, it may be additive to have 1.2 million spread across 3 proteins. Otherwise, waiting one day for that person's cells to divide to 800,000 and a second day to cross 1 million—but that would likely be too late for survival.
Ebola Zaire 1976 (Mayinga) virus causes acute hemorrhagic fever characterized by high mortality. There are no current vaccines or effective therapeutic measures to protect individuals who are exposed to this virus. In addition, it is not known which genes are essential for evoking protective immunity and should therefore be included in a vaccine designed for human use. In this study, the GP, NP, VP24, VP30, VP35, and VP40 virion protein genes of the Ebola Zaire 1976 (Mayinga) virus were cloned and inserted into a Venezuelan equine encephalitis (VEE) virus replicon vector (VRep) as shown in
The Ebola virus genes were sequenced from the VEE replicon clones and are listed here as SEQ ID NO:1 (GP), 2 (NP), 3 (VP24), 4 (VP30), 5 (VP35), 6 (VP40), and 7 (VP30#2) as described below. The corresponding amino acid sequences of the Ebola proteins expressed from these replicons are listed as SEQ ID NO: 17, 18, 19, 20, 21, 22, and 23, respectively. Changes in the DNA sequence relative to the sequence published by Sanchez et al. (1993) are described relative to the nucleotide (nt) sequence number from GenBank (accession number L11365).
The sequence we obtained for Ebola virus GP (SEQ ID NO:1) differed from the GenBank sequence by a transition from A to G at nt 8023. This resulted in a change in the amino acid sequence from Ile to Val at position 662 (SEQ ID NO: 17).
The DNA sequence we obtained for Ebola virus NP (SEQ ID NO:2) differed from the GenBank sequence at the following 4 positions: insertion of a C residue between nt 973 and 974, deletion of a G residue at nt 979, transition from C to T at nt 1307, and a transversion from A to C at nt 2745. These changes resulted in a change in the protein sequence from Arg to Glu at position 170 and a change from Leu to Phe at position 280 (SEQ ID NO: 18).
The Ebola virus VP24 (SEQ ID NO:3) gene differed from the GenBank sequence at 6 positions, resulting in 3 nonconservative changes in the amino acid sequence. The changes in the DNA sequence of VP24 consisted of a transversion from G to C at nt 10795, a transversion from C to G at nt 10796, a transversion from T to A at nt 10846, a transversion from A to T at nt 10847, a transversion from C to G at nt 11040, and a transversion from C to G at nt 11041. The changes in the amino acid sequence of VP24 consisted of a Cys to Ser change at position 151, a Leu to His change at position 168, and a Pro to Gly change at position 233 (SEQ ID NO: 19).
We have included 2 different sequences for the Ebola virus VP30 gene (SEQ ID NOS:4 and SEQ ID NO:7). Both of these sequences differ from the GenBank sequence by the insertion of an A residue in the upstream noncoding sequence between nt 8469 and 8470 and an insertion of a T residue between nt 9275 and 9276 that results in a change in the open reading frame of VP30 and VP30#2 after position 255 (SEQ ID NOS:20 and SEQ ID NO:23). As a result, the C-terminus of the VP30 protein differs significantly from that previously reported. In addition to these 2 changes, the VP30#2 gene in SEQ ID NO:23 contains a conservative transition from T to C at nt 9217. Because the primers originally used to clone the VP30 gene into the replicon were designed based on the GenBank sequence, the first clone that we constructed (SEQ ID NO:4) did not contain what we believe to be the authentic C-terminus of the protein. Therefore, in the absence of the VP30 stop codon, the C-terminal codon was replaced with 37 amino acids derived from the vector sequence. The resulting VP30 construct therefore differed from the GenBank sequence in that it contained 32 amino acids of VP30 sequence (positions 256 to 287, SEQ ID NO:20) and 37 amino acids of irrelevant sequence (positions 288 to 324, SEQ ID NO:20) in the place of the C-terminal 5 amino acids reported in GenBank. However, inclusion of 37 amino acids of vector sequence in place of the C-terminal amino acid (Pro, SEQ ID NO:23) did not inhibit the ability of the protein to serve as a protective antigen in BALB/c mice. We have also determined that a VEE replicon construct (SEQ ID NO:7), which contains the authentic C-terminus of VP30 (VP30#2, SEQ ID NO:23), is able to protect mice against a lethal Ebola challenge.
The DNA sequence for Ebola virus VP35 (SEQ ID NO:5) differed from the GenBank sequence by a transition from T to C at nt 4006, a transition from T to C at nt 4025, and an insertion of a T residue between nt 4102 and 4103. These sequence changes resulted in a change from a Ser to a Pro at position 293 and a change from Phe to Ser at position 299 (SEQ ID NO:21). The insertion of the T residue resulted in a change in the open reading frame of VP35 from that previously reported by Sanchez et al. (1993) following amino acid number 324. As a result, Ebola virus VP35 encodes for a protein of 340 amino acids, where amino acids 325 to 340 (SEQ ID NO:21) differ from and replace the C-terminal 27 amino acids of the previously published sequence.
Sequencing of VP30 and VP35 was also performed on RT/PCR products from RNA derived from cells that were infected with Ebola virus 1976, Ebola virus 1995 or the mouse-adapted Ebola virus. The changes noted above for the VRep constructs were also found in these Ebola viruses. Thus, we believe that these changes are real events and not artifacts of cloning.
The Ebola virus VP40 differed from the GenBank sequence by a transversion from a C to G at nt 4451 and a transition from a G to A at nt 5081. These sequence changes did not alter the protein sequence of VP40 (SEQ ID NO:22) from that of the published sequence.
To evaluate the protective efficacy of individual Ebola virus proteins and to determine whether the major histocompatibility (MHC) genes influence the immune response to Ebola virus antigens, two MHC-incompatible strains of mice were vaccinated with VRPs expressing an Ebola protein. As controls for these experiments, some mice were injected with VRPs expressing the nucleoprotein of Lassa virus or were injected with phosphate-buffered saline (PBS). Following Ebola virus challenge, the mice were monitored for morbidity and mortality, and the results are shown in Table 1.
The GP, NP, VP24, VP30, and VP40 proteins of Ebola virus generated either full or partial protection in BALB/c mice, and may therefore be useful components of a vaccine for humans or other mammals. Vaccination with VRPs encoding the NP protein afforded the best protection. In this case, 100% of the mice were protected after three inoculations and 95% of the mice were protected after two inoculations. The VRP encoding VP24 also protected 90% to 95% of BALB/c mice against Ebola virus challenge. In separate experiments (Table 2), two or three inoculations with VRPs encoding the VP24 protein protected BALB/c mice from a high dose (1×105 plaque—forming units (3×106 LD50)) of mouse-adapted Ebola virus.
Example 1 shows that vaccination with VRPs encoding GP protected 52-70% of BALB/c mice. The lack of protection was not due to a failure to respond to the VRP encoding GP, as all mice had detectable Ebola virus-specific serum antibodies after vaccination. Improved results were later seen, which are thought to be dose-dependent. Further, as shown in Examples 6-8, combining suboptimal formulations gives dramatically better protection.
Also in Example 1, some protective efficacy was further observed in BALB/c mice vaccinated two or three times with VRPs expressing the VP30 protein (55% and 85%, respectively),or the VP40 protein (70% and 80%, respectively). The VP35 protein was not efficacious in the BALB/c mouse model, as only 20% and 26% of the mice were protected after either two or three doses, respectively. Again, improved results were later seen, which are thought to be dose-dependent; and we found that combining suboptimal formulations gives dramatically better protection (e.g., combination of VP24, VP30 and VP40).
Geometric mean titers of viremia were markedly reduced in BALB/c mice vaccinated with VRPs encoding Ebola virus proteins after challenge with Ebola virus, indicating an ability of the induced immune responses to reduce virus replication (Table 1A). In this study, immune responses to the GP protein were able to clear the virus to undetectable levels within 4 days after challenge in some mice.
When the same replicons were examined for their ability to protect C57BL/6 mice from a lethal challenge of Ebola virus, only the GP, NP, and VP35 proteins were efficacious (Table 1B). The best protection, 95% to 100%, was observed in C57BL/6 mice inoculated with VRPs encoding the GP protein. Vaccination with VRPs expressing NP protected 75% to 80% of the mice from lethal disease. In contrast to what was observed in the BALB/c mice, the VP35 protein was the only VP protein able to significantly protect the C57BL/6 mice. In this case, 3 inoculations with VRPs encoding VP35 protected 70% of the mice from Ebola virus challenge. The reason behind the differences in protection in the two mouse strains is believed to be due to the ability of the immunogens to sufficiently stimulate the cellular immune system. As with the BALB/c mice, the effects of the induced immune responses were also observed in reduced viremias and, occasionally, in a prolonged time to death of C57BL/6 mice.
Example 4 shows that VRPs expressing Ebola virus GP or NP were also evaluated for protective efficacy in a guinea pig model. Sera from vaccinated animals were assayed for antibodies to Ebola by western blotting, IFA, plaque-reduction neutralization, and ELISA. Vaccination with either VRP (GP or NP) induced high titers of antibodies to the Ebola proteins (Table 4) in both guinea pig strains. We later found that VP40 induced high titers (4 logs) in mice. Neutralizing antibody responses were only detected in animals vaccinated with the VRP expressing GP (Table 4).
As shown in Example 4, vaccination of strain 2 inbred guinea pigs with the GP construct protected 3/5 animals against death from lethal Ebola challenge, and significantly prolonged the mean day of death in one of the two animals that died (Table 4). All of the strain 13 guinea pigs vaccinated with the GP construct, alone or in combination with NP, survived lethal Ebola challenge (Table 4). Vaccination with NP alone did not protect either guinea pig strain from challenge with the guinea pig-adapted Ebola virus. Of note, guinea pigs are also inbred, and the failure of NP to protect may indicate that they could not respond with appropriate T cells, but could make protective antibodies to GP. This is further support for our preferred embodiments including multiple peptides and proteins, and even all six of the Ebola proteins.
As shown in Example 3, to identify the immune mechanisms that mediate protection against Ebola virus and to determine whether antibodies are sufficient to protect against lethal disease, passive transfer studies were performed. One mL of immune sera, obtained from mice previously vaccinated with one of the Ebola virus VRPs, was passively administered to unvaccinated mice 24 hours before challenge with a lethal dose of mouse-adapted Ebola virus. Antibodies to GP, but not to NP or the VP proteins, protected mice from an Ebola virus challenge (Table 3). Antibodies to GP protected 75% of the BALB/c mice and 85% of the C57BL/6 mice from death. When the donor sera were examined for their ability to neutralize Ebola virus in a plaque-reduction neutralization assay, a 1:20 to 1:40 dilution of the GP-specific antisera reduced the number of viral plaque-forming units by at least 50% (data not shown). In contrast, antisera to the NP and VP proteins did not neutralize Ebola virus at a 1:20 or 1:40 dilution. These results are consistent with the finding that GP is the only viral protein found on the surface of Ebola virus, and is likely to induce virus-neutralizing antibodies.
As shown in Examples 5 and 6, cince the NP and VP proteins of Ebola virus are internal virion proteins to which antibodies are not sufficient for protection, it is likely that cytotoxic T lymphocytes (CTLs) are also important for protection against Ebola virus. The inventors investigated cellular immune responses to individual Ebola virus proteins expressed from VRPs identified CTL responses to the VP24 and NP proteins (Table 5). One CTL epitope that we identified for the Ebola virus NP is recognized by C57BL/6 (H-2b) mice, and has an amino acid sequence of, or contained within, the following 11 amino acids: VYQVNNLEEIC (SEQ ID NO:24). Vaccination with EboNPVRP and in vitro restimulation of spleen cells with this peptide consistently induces strong CTL responses in C57BL/6 (H-2b) mice. In vivo vaccination to Ebola virus NP is required to detect the CTL activity, as evidenced by the failure of cells from C57BL/6 mice vaccinated with Lassa NP to develop lytic activity to peptide (SEQ ID NO:24) after in vitro restimulation with it. Specific lysis has been observed using very low effector:target ratios (<2:1). This CTL epitope is H-2b restricted in that it is not recognized by BALB/c (H-2d) cells treated the same way (data not shown), and H-2b effector cells will not lyse MHC-mismatched target cells coated with this peptide.
A CTL epitope in the VP24 protein was also identified. It is recognized by BALB/c (H-2d) mice, and has an amino acid sequence of, or contained within, the following 23 amino acids: LKFINKLDALLVVNYNGLLSSIF (SEQ ID NO:25). In the data shown in Table 5, high (>90%) specific lysis of P815 target cells coated with this peptide was observed. The background lysis of cells that were not peptide-coated was also high (>50%), which is probably due to the activity of natural killer cells. We are planning to repeat this experiment using the L5178Y target cells, which are not susceptible to natural killer cells. This shows that CTLs mediated protection, which is further demonstrated by the evidence in Examples 6, 7 and 8.
Olinger, Jr., Gene Garrard, Bailey, Michael Adam, Hart, Mary Katherine, Wilson, Julie Ann
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